1. Field
This disclosure relates generally to pressure sensors, and more specifically, to a pressure sensor having a “teeter totter” design that provides a differential capacitive output signal.
2. Related Art
Modern vehicles are increasingly using sensors to determine whether there is adequate air pressure in the vehicle's tires. Direct tire pressure monitoring using in-tire pressure sensors with a radio frequency (RF) data link are typically used to measure tire pressure.
In one type of tire pressure monitoring system (TPMS), a micro-electromechanical systems (MEMS) pressure sensor device configured to sense a pressure stimulus that is external to the MEMS pressure sensor device is utilized. Such MEMS pressure sensor devices measure pressure changes capacitively, using a diaphragm exposed to the external environment as one electrode of a sense capacitor with the other electrode of the sense capacitor being fixed. In this manner, the diaphragm deforms as external pressure changes, thereby changing the capacitive signal. One drawback of such a system is that changes in the signal are non-linear due to the inverse relationship between capacitance and the distance between capacitor plates. Another drawback of such system is that the output signal is weak compared to other types of MEMS sensors that provide a differential capacitance output.
It is therefore desirable to have a pressure sensor device that provides a more linear output signal in relation to external pressure changes, and that the output signal be derived from a differential capacitance so as to increase the signal level.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.